In an article entitled "Epitaxial Photodetector Catches Optical Signals", published in Electronic Design, Volume 25, Page 102 (Dec. 6, 1977), AEG-Telefunken has described an epitaxial GaAlAs (gallium-aluminum arsenide) detector which has holes etched in the top and bottom thereof to permit the two ends of an optical fiber data line to be inserted and cemented. The article indicates that a transparent photodetector can provide a simple means of picking off optical signals in the middle of a fiber optic data link. Further, signals can be picked off more easily than by using an optical branching unit or by breaking a fiber and inserting a detector along with an amplifier for driving a second light source to relaunch the signals. Notwithstanding this article, however, it is sometimes necessary and important to insert, or inject, information onto the data line as well as monitor the data on the line.
This prior art discloses that the transmission efficiency of the detector approaches 70% and that the layers between the fiber ends are less than 10 micrometers thick, providing useful through transmission. The ability to inject as well as monitor data would greatly increase the potential usefulness of such a device. According to the present invention, an epitaxial GaAlAs detector/LED transceiver is disclosed which includes modulation of a light beam injected at one end of the data line or by LED (Light Emitting Diode) injection of a light signal.